<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>可选链操作符</title>
  </head>
  <body>
    <script>
      // ?.
      function main(config) {
        // const dbHost = config && config.db && config.db.host;
        const dbHost = config?.db?.host;

        console.log(dbHost);
      }

      main({
        db: {
          host: "192.168.1.100",
          username: "root",
        },
        cache: {
          host: "192.168.1.200",
          username: "admin",
        },
      });
    </script>
  </body>
</html>
